1. Field of the Invention
This invention relates to a new magnetic recording medium having improved electromagnetic conversion characteristics.
2. Description of Prior Arts
An audio cassette tape, specifically for recording music is required particularly to have excellent electromagnetic conversion characteristics. For instance, the audio cassette tape for recording music ought to be high not only in the maximum distorted power output at 315 Hz (hereinafter referred to as MOL 315) but also in the maximum power output at 10 KHz (hereinafter referred to as SOL 10K) and further ought to be low in bias noise (hereinafter referred to as BN).
As for a video cassette tape, it ought to give a reproduced sound of a high quality in the high-density reconding ssystem such as that employed in the threefoldspeed tape traveling mode.
Thus, a magnetic recording medium such as audio tape or video tape is under requirement to improve electromagnetic conversion characteristics thereof.
Heretofore, there have been proposed a variety of measures for the improvement of the magnetic conversion characteristics of a magnetic recording medium, for example, through improvements with respect to the ferromagnetic powder, binder composition, dispersability of the ferromagnetic powder in the binder, orientation of the ferromagnetic powder in the magnetic recording layer.
It has been known that the electromagnetic conversion characteristics are improved by increasing the residual magnetic flux density (hereinafter referred to as Br), as is described in "Hi-Fi Tape Recorder" edited by Masahiko Morizono (Radio Technology Corp., Japan). The residual magnetic flux density increases as the squareness ratio increases. The increase of the squareness ratio is accomplished by increasing a packing density of the ferromagnetic powder in the magnetic recording layer.
The previously proposed measures for the improvement of the electromagnetic conversion characteristics are still under restrictions. For instance, the residual magnetic flux density can be increased only up to a certain limit defined by nature of the ferromagnetic powder. Accordingly, the improvement of the electromagnetic conversion characteristics based on the improvement of the residual magnetic flux density is under restriction.
It may be thought that enhancement of the coercive force (hereinafter referred to as Hc) of the magnetic recording layer brings about enhancement of SOL 10K through reduction of self-demagnetizing force. However, the enhancement of the coercive force makes the recording bias deeper or broader to increase loss in the low frequency range, whereby MOL 315 lowers. Therefore, the coercive force has to be adjusted to give a satisfactory balance between MOL 315 and SOL 10K. Thus, the increase of coercive force only is not satisfactory to give a magnetic recording medium having electromagnetic conversion characteristics in the whole area from a low frequency range to a high frequency range.
A measure of balancing the residual magnetic flux density and the coercive force is not satisfactorily effective to enhance effective value of the recording bias.
Accordingly, the prior arts hardly provide a magnetic recording medium having satisfactorily high MOL 315 value and SOL 10K value.